path: root/Documentation/libtracefs-dynevents.txt

libtracefs(3)
=============

NAME
----
tracefs_dynevent_create, tracefs_dynevent_destroy, tracefs_dynevent_destroy_all,
tracefs_dynevent_free, tracefs_dynevent_list_free, tracefs_dynevent_get, tracefs_dynevent_get_all,
tracefs_dynevent_info, tracefs_dynevent_get_event - Create, destroy, free and get dynamic events.

SYNOPSIS
--------
[verse]
--
*#include <tracefs.h>*

struct *tracefs_dynevent*;
enum *tracefs_dynevent_type*;
int *tracefs_dynevent_create*(struct tracefs_dynevent pass:[*]_devent_);
int *tracefs_dynevent_destroy*(struct tracefs_dynevent pass:[*]_devent_, bool _force_);
int *tracefs_dynevent_destroy_all*(unsigned int _types_, bool _force_);
void *tracefs_dynevent_free*(struct tracefs_dynevent pass:[*]_devent_);
void *tracefs_dynevent_list_free*(struct tracefs_dynevent pass:[*]pass:[*]_events_);
struct tracefs_dynevent pass:[*]*tracefs_dynevent_get*(enum tracefs_dynevent_type _type_, const char pass:[*]_system_, const char pass:[*]_event_);
struct tracefs_dynevent pass:[*]pass:[*]*tracefs_dynevent_get_all*(unsigned int _types_, const char pass:[*]_system_);
enum tracefs_dynevent_type *tracefs_dynevent_info*(struct tracefs_dynevent pass:[*]_dynevent_, char pass:[*]pass:[*]_system_, char pass:[*]pass:[*]_event_, char pass:[*]pass:[*]_prefix_, char pass:[*]pass:[*]_addr_, char pass:[*]pass:[*]_format_);
struct tep_event pass:[*]*tracefs_dynevent_get_event*(struct tep_handle pass:[*]_tep_, struct tracefs_dynevent pass:[*]_dynevent_);
--

DESCRIPTION
-----------

The *tracefs_dynevent_create*() function creates dynamic event _devent_ in the system.

The *tracefs_dynevent_destroy*() function removes dynamic event _devent_ from the system. If _force_
is true, the function will attempt to disable all events in all trace instances, before removing
the dynamic event. The _devent_ context is not freed, use *tracefs_dynevent_free*() to free it.

The *tracefs_dynevent_destroy_all*() function removes all dynamic events of given types from the
system. The _types_ parameter is a type of specific dynamic event, or a bitmask of dynamic events
types *tracefs_dynevent_type*, that will be removed. If _types_ is 0, dynamic events from all types
will be removed.  If _force_ is true, the function will attempt to disable all events in all trace
instances, before removing the dynamic events.

The *tracefs_dynevent_get*() function allocates and returns a single instance of a dynamic
event that matches the given *type*, *system* and *event* that is passed to it. NULL is returned
if there is no match. The returned event is what is found in the system, and must be freed
with *tracefs_dynevent_free*(). If *system* is NULL, then the first *event* of any system
of the given type that has the name of *event* will be returned.

The *tracefs_dynevent_get_all*() function allocates and returns an array of pointers to dynamic
events of given types that exist in the system. The last element of the array is a NULL pointer.
The array must be freed with *tracefs_dynevent_list_free*(). If there are no events a NULL pointer is
returned. The _types_ parameter is a type of specific dynamic event, or a bitmask of dynamic events
types *tracefs_dynevent_type*, that will be retrieved. If _types_ is 0, dynamic events from all
types will be retrieved.

The *tracefs_dynevent_free*() function frees a dynamic event context _devent_.

The *tracefs_dynevent_list_free*() function frees an array of pointers to dynamic event, returned
by *tracefs_dynevent_get_all()* API.

The *tracefs_dynevent_info*() function returns the type and information of a given dynamic event
_dynevent_. If any of the _system_, _event_, _prefix_, _addr_ or _format_ arguments are not NULL,
then strings are allocated and returned back via these arguments. The _system_ and _event_ holds the
system and the name of the dynamic event. If _prefix_ is non NULL, then it will hold an allocated
string that holds the prefix portion of the dynamic event (the content up to the ":", exluding it).
If _addr_ is non NULL, it will hold the address or function that the dynamic event is attached to,
if relevant for this event type. If _format_ is non NULL, it will hold the format string of the
dynamic event. Note, that the content in _group_, _event_, _prefix_, _addr_, and _format_ must be
freed with free(3) if they are set.

The *tracefs_dynevent_get_event*() function returns a tep event, describing the given dynamic event.
The API detects any newly created or removed dynamic events. The returned pointer to tep event is
controlled by @tep and must not be freed.

RETURN VALUE
------------

*tracefs_dynevent_create*() returns 0 on success, or -1 on error. If a parsing error occurs then
*tracefs_error_last*(3) may be used to retrieve the error message explaining the parsing issue.

*tracefs_dynevent_destroy*() and *tracefs_dynevent_destroy_all*() return 0 on success, or -1 on
error. If _force_ is enabled, the functions may fail on disabling the events.

*tracefs_dynevent_get*() function returns an allocated dynamic event from the system that matches
the type, system and event given.

*tracefs_dynevent_get_all*() function returns allocated array of pointers to dynamic events, or NULL
in case of an error or in case there are no events in the system. That array must be freed by
*tracefs_dynevent_list_free*().

*tracefs_dynevent_info*() returns the type of the given dynamic event  or TRACEFS_DYNEVENT_UNKNOWN
on error. If _system_, _event_, _prefix_, _addr_, or _format_ are non NULL, they will contain
allocated strings that must be freed by free(3).

The *tracefs_dynevent_get_event*() function returns a pointer to a tep event or NULL in case of an
error or if the requested dynamic event is missing. The returned pointer to tep event is controlled
by @tep and must not be freed.

ERRORS
------
The following errors are for all the above calls:

*ENODEV* dynamic events of requested type are not configured for the running kernel.

*ENOMEM* Memory allocation error.

*tracefs_dynevent_create*() can fail with the following errors:

*EINVAL*  Most likely a parsing error occurred (use *tracefs_error_last*(3) to possibly
          see what that error was).

Other errors may also happen caused by internal system calls.

EXAMPLE
-------
[source,c]
--
#include <stdlib.h>
#include <unistd.h>
#include <sys/wait.h>

#include <tracefs.h>

static struct tep_event *open_event;
static struct tep_format_field *file_field;

static struct tep_event *openret_event;
static struct tep_format_field *ret_field;

static int callback(struct tep_event *event, struct tep_record *record,
		    int cpu, void *data)
{
	struct trace_seq seq;

	trace_seq_init(&seq);
	tep_print_event(event->tep, &seq, record, "%d-%s: ", TEP_PRINT_PID, TEP_PRINT_COMM);

	if (event->id == open_event->id) {
		trace_seq_puts(&seq, "open file='");
		tep_print_field(&seq, record->data, file_field);
		trace_seq_puts(&seq, "'\n");
	} else if (event->id == openret_event->id) {
		unsigned long long ret;
		tep_read_number_field(ret_field, record->data, &ret);
		trace_seq_printf(&seq, "open ret=%lld\n", ret);
	} else {
		goto out;
	}

	trace_seq_terminate(&seq);
	trace_seq_do_printf(&seq);
out:
	trace_seq_destroy(&seq);

	return 0;
}

static pid_t run_exec(char **argv, char **env)
{
	pid_t pid;

	pid = fork();
	if (pid)
		return pid;

	execve(argv[0], argv, env);
	perror("exec");
	exit(-1);
}

const char *mykprobe = "my_kprobes";

int main (int argc, char **argv, char **env)
{
	struct tracefs_dynevent *kprobe, *kretprobe;
	const char *sysnames[] = { mykprobe, NULL };
	struct tracefs_instance *instance;
	struct tep_handle *tep;
	pid_t pid;

	if (argc < 2) {
		printf("usage: %s command\n", argv[0]);
		exit(-1);
	}

	instance = tracefs_instance_create("exec_open");
	if (!instance) {
		perror("creating instance");
		exit(-1);
	}

	tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_KPROBE | TRACEFS_DYNEVENT_KRETPROBE, true);

	kprobe = tracefs_kprobe_alloc(mykprobe, "open", "do_sys_openat2",
				      "file=+0($arg2):ustring flags=+0($arg3):x64 mode=+8($arg3):x64\n");
	kretprobe = tracefs_kretprobe_alloc(mykprobe, "openret", "do_sys_openat2", "ret=%ax", 0);
	if (!kprobe || !kretprobe) {
		perror("allocating dynamic events");
		exit(-1);
	}

	if (tracefs_dynevent_create(kprobe) || tracefs_dynevent_create(kretprobe)){
		char *err = tracefs_error_last(NULL);
		perror("Failed to create kprobes:");
		if (err && strlen(err))
			fprintf(stderr, "%s\n", err);
		exit(-1);
	}

	tep = tracefs_local_events_system(NULL, sysnames);
	if (!tep) {
		perror("reading events");
		exit(-1);
	}
	open_event = tep_find_event_by_name(tep, mykprobe, "open");
	file_field = tep_find_field(open_event, "file");

	openret_event = tep_find_event_by_name(tep, mykprobe, "openret");
	ret_field = tep_find_field(openret_event, "ret");

	tracefs_event_enable(instance, mykprobe, NULL);
	pid = run_exec(&argv[1], env);

	/* Let the child start to run */
	sched_yield();

	do {
		tracefs_load_cmdlines(NULL, tep);
		tracefs_iterate_raw_events(tep, instance, NULL, 0, callback, NULL);
	} while (waitpid(pid, NULL, WNOHANG) != pid);

	/* Will disable the events */
	tracefs_dynevent_destroy_all(TRACEFS_DYNEVENT_KPROBE | TRACEFS_DYNEVENT_KRETPROBE, true);
	tracefs_dynevent_free(kprobe);
	tracefs_dynevent_free(kretprobe);
	tracefs_instance_destroy(instance);
	tep_free(tep);

	return 0;
}
--

FILES
-----
[verse]
--
*tracefs.h*
	Header file to include in order to have access to the library APIs.
*-ltracefs*
	Linker switch to add when building a program that uses the library.
--

SEE ALSO
--------
*libtracefs*(3),
*libtraceevent*(3),
*trace-cmd*(1)

AUTHOR
------
[verse]
--
*Steven Rostedt* <rostedt@goodmis.org>
*Tzvetomir Stoyanov* <tz.stoyanov@gmail.com>
*Yordan Karadzhov* <y.karadz@gmail.com>
--
REPORTING BUGS
--------------
Report bugs to  <linux-trace-devel@vger.kernel.org>

LICENSE
-------
libtracefs is Free Software licensed under the GNU LGPL 2.1

RESOURCES
---------
https://git.kernel.org/pub/scm/libs/libtrace/libtracefs.git/

COPYING
-------
Copyright \(C) 2021 VMware, Inc. Free use of this software is granted under
the terms of the GNU Public License (GPL).